The Greatest Soldier of the 20th century. The father of Solid, Liquid and Solidus Snake, resulting from the Les Enfants Terribles (The terrible children) project. Originally known as Naked Snake, he earned the name Big Boss after defeating his mentor, the Boss, during Operation Snake Eater. Lost his right eye during said operation.

Founded FOXHOUND in the early 1970s, he subsequently betrayed the United States, probably due to their betrayal of his mentor. Founded Outer Heaven and built Metal Gear, a nuclear-equipped walking battle tank, based on an earlier version which he himself had destroyed. Was defeated by his son, Solid Snake and went into hiding until 4 years later when he became general commander of Zanzibar land. Was defeated by Snake in hand-to-hand combat.

You are a true patriot. Higher than the Boss. You are hereby awarded the title of Big Boss.

Solid Snake's biological father. Commonly portrayed as a very old man in a suit underneath a khaki trenchcoat, and wearing an eyepatch on his right eye.
Big Boss is deceased really. However, the US government has managed to preserve his incinerated remains, and with this, they can study his genetic code. And by studying his genetic code, they can find out what genes caused Big Boss to be "the greatest soldier of the 20th century"; these genes are called the "soldier genes".
Big Boss's genetic legacies were going to be octuplets, but 6 were intentionally aborted so that Solid Snake and Liquid Snake would grow to be incredibly strong. However, Solidus was the survivor of the abortion, and is thus the third.

Big Boss fought Solid Snake twice, once in the first Metal Gear game (set in Outer Heaven), and the second Metal Gear game (set in Zanzibar Land).
It is highly possible that Solid Snake is Big Boss's greatest genetic legacy, despite their hatred before BB's death. After all, who else could take out an almost-immortal soldier (Liquid Snake that is)?!

It has been suggested that Big Boss is the main character for Metal Gear Solid 3 : Snake Eater. We won't know until the game is released in November of 2004....

"Whoever wins, the battle does not end. The loser is freed from the battlefield, the winner must remain there, and the survivor must live his life as the warrior until he dies."
-Big Boss, Metal Gear 2 : Solid Snake

"This philosophy is why I don't fight.....to me it means that if I got in a fight and managed to win, there will always be people coming after me to try to kill me. No matter how many times I win, there will ALWAYS be people after me. It's a cruel world..."
-me

Big Boss is the main character of Metal Gear Solid 3: Snake Eater, and Metal Gear Solid: Portable Ops.
His birth name is Jack.
Jack was born sometime in the 1930's (Date Unknown). In the early 1950's Jack joined the Green Berets and became The Boss's apprentice (The boss is hero from WWII). In 1954, Jack was involved in the first airborne detonation of a hydrogen bomb. The Boss taught him everything about combat, from weaponry, survival, espionage, destruction, psychology. She taught him to speak Russian as well. He and The Boss developed a combat technique called CQC (Close Quarters Combat). His mentor, friend, and lover, The Boss left for unknown reasons on June 12 1959.

On August 24th, 1964, Jack was part of an operation entitled the "Virtuous Mission", in which he was to rescue a defecting Soviet rocket scientist named Nikolai Stepanovitch Sokolov. It was during this mission that Jack was given the codename "Naked Snake." Naked Snake deriving from the fact that he was there with no weapons, food, or backup assistance, he was "Naked" just as him name implied. "Snake" came from the fact that he was a student of The Boss which was a member of the COBRA unit, a unit responsible for the Allies victory in WWII.
However, this mission failed, due to the defection of The Boss. It is later discovered that The Boss had not truly defected, but that she was acting as a double agent to retrieve the Philosophers' Legacy (A large amount of hidden wealth) from Volgin.
A week later, FOX unit and Snake were assigned "Operation Snake Eater", in which the objective was to eliminate The Boss and her new Soviet ally, Colonel Volgin, rescue Sokolov & destroy the Shagohod. It was during this mission that Snake came across the prototype designs for the Metal Gear TX-55 bipedal tank from Granin, who was sending them to a colleague in America. This colleague was presumably the grandfather of Hal Emmerich, aka Otacon
During this mission, Snake had his right eye accidentally damaged by the muzzle flash from Ocelot's Colt Single Action Army, while in captivity for torture, in order to save EVA's life. However, he succeeded in completing the mission, and killed The Boss and Colonel Volgin. For this, he was awarded the code name Big Boss and the Distinguished Service Cross by President Lyndon B. Johnson.
Big Boss, however, was heavily affected by Operation: Snake Eater, thanks to the fact that he had to kill his old mentor, The Boss, and after finding out that the whole operation was a rouse set up by his government to avoid taking the blame for a nuclear attack while secretly getting their hands on the Philosophers' Legacy, Big Boss lost sight of what he was fighting for, and with it, his patriotism for his country. Because of this, he decided to retire from FOX.
When direct American involvement in the Vietnam conflict started the following year, Big Boss participated in Long Range Reconnaissance Patrol (LRRP) along with teams of Green Berets and Army Rangers. His skills in combat earned him the "great legendary soldier" moniker. Once the conflict had ended, Big Boss took part in more than 70 missions attached to groups such as the SOG (Studies and Observation Group), the Wild Geese (a mercenary unit), and the Delta Force (an elite counter-terrorist unit created in 1977). He also met up with a war orphan named Frank Jaeger at Mozambique in 1966, and escorted the child to an orphanage where he could be taken care of.
It was around this time that Big Boss was found to be infertile due to the Bikini Atoll testing he had taken part in years earlier.

San Hieronymo Takeover

Naked Snake (Big Boss), during the FOX unit's revolt, circa 1970.
In 1970, the FOX unit was considered rogue after its members organized a revolt and took over a base in South America known as "La Peninsula De Los Muertos". Big Boss was taken prisoner by Cunningham (a member of FOX).
Meeting a member of the Green Berets who was sent to take care of FOX going by the name of Roy Campbell, the two managed to persuade various members of the Red Army which FOX were commanding, to join forces with them and rise up against the renegade members, forming the early beginnings of what would become FOXHOUND. Para-Medic and Sigint also helped Boss in defeating FOX and clearing their names, as well as Major Zero's (who were all partially blamed for the up-rising). Afterwards, Big Boss officially formed FOXHOUND, to carry on the tradition of the FOX unit and to give a home to the soldiers he had recruited during the San Hyeronimo Incident.
While there, Big Boss once again met Frank Jaeger, this time going under the code-name Null. The two fought on a number of separate occasions and after the incident Big Boss adopted Null and recruited him to FOXHOUND under a new code-name, "Gray Fox". He also met Python once again, who had in fact not died during the Vietnam War but was kept alive by the CIA and trained as an "anti-Snake" knowing that Python knew a lot about Big Boss' fighting style. Big Boss did not kill Python but defeated him and recruited him.

Les Enfants Terribles & The Patriots

Ocelot and Major Zero later extended an invitation to Big Boss to join them in the forming of a new organization known as "The Patriots." This organization was to be set up in honor of The Boss' last wish. Big Boss, who knew her better than anyone else, was chosen by Zero to be an icon, a hero, to the world. Zero wanted to turn Big Boss into a legend, and started spreading stories about him, some true, some exaggerated, and some outright lies. Big Boss later became infuriated with Zero's lust for power, and was sick of playing the role of a puppet.
Afraid of losing Big Boss, Zero planned a secret project. In 1972, Big Boss was found in a coma and Zero brought his unconscious body to a lab where his genes were extracted to make genetically enhanced soldiers. This project would be known as "Les Enfants Terribles project." Liquid Snake, Solid Snake, and Solidus Snake were produced in this program, and were known as the "Sons of Big Boss." However, this was the final straw between the two, and Big Boss left The Patriots, determined to oppose them. He left the United States, drifting around the world, before finally deciding to create his own and created the fortress and philosophical idea known as Outer Heaven. Big Boss also returned to the US to covertly take command his special forces unit FOXHOUND.

The main character of Metal Gear Solid 3: Snake Eater. In the 70s he falls in a coma, so the pentagon takes his DNA, and they create three clones. (Solid, Liquid and Solidus Snake --> He is the youngest, but seems the oldest)The project was called "Las enfants terribles"(this means the terrible children and also was called Eve project) In the 80s he losses his eye and goes in retirement, then he trained other soldiers. He also becomes the of Fox-Hound.
He simply was the best solider who ever lived.

Big Boss is the greatest soldier who ever lived and he's better then Solid Snake!!!